ASP and ASP.NET are NOT! the same thing. Some people enable ASP
hoping that ASP.NET will work also, this is just not the case. IIS 6.0 comes
with ASP.NET disabled by default, and this will show you how to enable it.

In this window, select "ASP.NET" (which will put a checkmark
next to it) and click "OK", then "Next" and "Finish"

At this point your ASP.NET pages should work, and we're just
going to make sure that the Web Service Extension is enabled in the IIS Manager.
Now, load IIS from the Administrative tools in the Control Panel by clicking
Start -> Administrative Tools -> IIS Manager (or loading the Control Panel,
entering the Administrative Tools folder, and double clicking IIS Manager)

Expand your computer name and click on "Web Service Extensions".
Make sure "ASP.NET" has a checkmark next to it, and that means that it's enabled